Various publications are referred to throughout this application. Citations for these references may be found at the end of the specification immediately preceding the claims. The disclosures of these publications are hereby incorporated by reference in their entireties into the subject application to more fully describe the art to which the subject application pertains.
Kidney diseases are estimated to affect up to 10 million people worldwide. Diabetic nephropathy (DNP) and focal segmental glomerulosclerosis (FSGS) are the two major causes of end-stage renal disease (ESRD), accounting for more than half of the ESRD cases in the US1. Diagnoses of FSGS and DNP are based on the clinical findings of proteinuria and histological scarring of the renal glomerulus, the major filtering apparatus of the kidney.
Podocytes, the visceral epithelial cells of the glomerulus, have recently taken center stage in research on the pathogenesis of FSGS. Genetic studies in both human and mouse reveal that the development of FSGS is initiated by podocyte dysfunction2. Inherited mutations is likely responsible for this disease in only a minor fraction of patients.
Diabetic nephropathy is characterized by mesangial expansion and thickening of the glomerular basement membrane leading to mesangial expansion and focal and nodular sclerosis of the glomerulus. Podocyte dysfunction has also repeatedly been reported in DNP7. The degree of albuminuria and the rate of progression correlates best with glomerular podocyte density in patients with diabetic nephropathy8. The mechanism of podocyte loss/dysfunction in DNP is under intense investigation; both cell detachment and apoptosis have been described as potential mechanisms9, 10. These events might even be linked as dead cells usually detach from the GBM and cells that detach usually die. As podocytes are terminally differentiated cells and unable to replicate, both of these mechanism can lead to decreased cell density. However, it has not been known whether protection from podocyte loss or dysfunction would influence glomerular disease development.
The Notch signaling pathway comprises a family of transmembrane receptors, their ligands, negative and positive modifiers, and transcription factors11, 12. To date, 4 mammalian receptors (Notch1 through Notch4) and at least 5 ligands (Delta 1, 3, and 4 and Jagged 1, 2) have been identified. Binding of the ligand renders the Notch receptor susceptible to metalloprotease- and γ-secretase-mediated proteolytic cleavage, which in turn results in the release of the Notch intracellular domain (ICN) from the plasma membrane and its subsequent translocation into the nucleus. Once there, ICN associates with DNA-binding protein recombination signal-binding protein Jκ/CBF1/Su (H)/Lag-1 (Rbpj) and mastermind-like (MAML) protein, which recruit additional factors with histone acetylase activity, such as p300 and p300/CREB-binding protein-associated factor. These proteins form a heteromeric complex that mediate transcription of target genes, including basic helix-loop-helix transcription factors of the hairy and enhancer of split (Hes) family and the Hes-related repressor protein (Hey) family13.
The Notch pathway plays a crucial role in podocyte development. Genetic deletion of presenilin, Notch2 or treatment of developing kidney explants with a γ-secretase inhibitor (GSI) leads to metanephric mesenchyme that produces nephrons without glomeruli, proximal tubules, and loops of Henle but contain distal tubules that are correctly fused to the collecting duct14-16. This may be due to the fact that cells in the absence of active Notch2 fail to proliferate and fail to downregulate Pax214. Patients with Alagille syndrome, who lack one copy of Notch2 present with similar renal developmental abnormalities as well17. Very little is known about Notch signaling in the kidney beyond renal development. While during development the kidney has one of the highest levels of Notch activity, very little Notch activity can be detected in the mature mouse kidney18.
Renal disease is currently treated using angiotensin inhibitors (ACE inhibitors) and angiotensin receptor blockers, although these treatments typically only slow progression of the disease. Accordingly, there is a need for new therapy to prevent and treat renal disease.